I poured my hearth slab today and ended up with a real rough texture. I used Sakrete brand baged concrete and once I was done, the surface texture felt like sandpaper. My previous concrete jobs (very small) left me with a creamy smooth surface after it was finished, but I could not get the same results with this slab. I had bleed water on the surface like I expected but when this water was reabsored into the concrete, I could not achieve a smooth texture. It's as if the sand in the mix is all at the top. I'm not worried about the texture but am concerned with the strength. Has anyone experienced this? I am thinking about using a patching compound to smooth it out. Any thoughts?

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SteveP
I am not familiar with your premixed cement products over there, we also have them here but I often have my doubts as to the proportions of the ingredients used and often the quantity of portland for that quantity seems too little in my mind.
I like to get my own sand, gravel (metal) and portland, mix the portland with water in the mixer, add the gravel and then finally the sand.
I always get maximum strength concrete using the measured proportion as recommended on the bags of cement.
As the portland is put in the water, it is liquid and thoroughly coats the gravel which is the bulking agent in concrete thoroughly and then the sand is added which fills in the gaps. You might need to add a little more water to attain the optimum 'slump' (viscosity) for pouring.
The surface being a little rougher, will only improve the bond of your vermicrete layer later.

My slabs were not so pretty, either. To hide my issues I used a broom finish as the final pass.

I have mixed a lot of the premix concrete stuff so far. First for the slab, hearth, and side foundations for the kitchen . Then the seating walls and columns. Wiley gave me some advise to add some portland to the mix and it would flow better into the columns. I added 2 to 3 shovel fulls to each batch (2 ea 80 lb bags) - I could really tell a difference in how creamy it was - especially when finishing off the exposed concrete at the top of the forms.

I believe I will continue this practice where cosmetics matter. Sounds like a little too much portland is not a terribly bad thing on the size of pours that we do to make a pizza oven stand.

The concrete for my foundataion was from a ready mix company and I did notice that the sand in the ready mix was finer than the sand in the bagged concrete and was easier to work. I did cover the hearth slab with a blanket and wet it down then covered it with a tarp to retain the moisture. I am planning on keeping it in this state for another week and a half.

I will be putting down some insulation. I am planning on using 2" board but haven't decided on what to use. I checked into SuperIsol boards but Armil hasn't gotten back with me yet. I'd like to use the FB board but the shipping is more than double the cost of the board last time I checked. I was really concerned with the strength of the slab since it has to bear a lot of weight, but everyone is reassuring me that it should be fine so I won't worry any longer about it.

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